Photometric device



April 6, 1954 F. F. CRANDELL PHOTOMETRIC DEVICE Filed May 21. 1949 FA/vz (BAA/DELL,

INVEN TOR.

Patented Apr. 6, 1954 UNITED STATES PATENT OFFICE.-

PHOTQMETRIC DEVI CE- FrankF. Crandell, Pasadena, Calif}, assignor-to Photo; Research Corporation, San Fernando; Califi, a corporation of California Application May. 21-, 1949, Serial No. 94,719- 10=Claims. (Cl. 8822.5)

This invention relates to a photometric device and is particularly directed to a simple, inexpensive, portable, light weight and compact device for rapidly and accurately determining colortemperature of light or correction filters which should beemployed during photographyfor the purpose of modifying the light reaching a photographic film in order to permit accurate color renditionv ofthe subject being photographed.

The invention, moreover, is directed to an arrangement of elements whe by a single photoelectric cell is employed forthe purpose ofsimultaneously generating different output currents.

In addition, the invention contemplates means amount on aggregate of light underwhich the;

subject is exposed and. when color-sensitive film is; used; it becomes necessary to know the particular color characteristics of the. light source. Light which has the same intensity may vary widely in its color temperature or spectral com-. position.

The color temperature of light is usually meas.- ured in degrees Kelvin, which is a measure of the temperature to which. a black body must be raised to have the same color as 'the light in dues: tion. Color-sensitive film is made for use under lightof a particular color temperature range, and true color rendition can only be obtained when the light employed is of thedesired color temp erature Once the. color temperature, of the light sou c s d t rmin a otog a h a then select a specific color-sensitive film which will match the temperature of theflight; time ma c n te o th a on. be w l h color temperature of the light source and the color temperature for which the film is designed by the use of selected filters, by supplementing the light source with light modifying the char-- acteri sticsof the initiallight source, or by modifying-the voltage of the light source being used.

A color temperature meter employing a single. photocell is. described in. copend application 2. Serial No. 49,706, filed September 17, 1948,, by

Frank F. Crandell-andHerman Heidt, now Patent 2,587,601, issued. March 4.., 19,52. The present inventionmay betermed to be an improvement on the direct-reading color temperature. meter.

there described, in. that, readings are obtained with greaterfacility. and although a single, cell is employed, the light impinging uponsuch. cell is modified byvtwolightl filters simultaneously.

It is an object of; thepresent invention, there;

fore, to disclose anddescribe asimple and efiectivedirectereading photometric instrument particularly. adapted to facilitatethe determination of color temperatureof light, the characteristics of a. film tobe. used with a given source of, light, or the. character of comp nsating, filters. to be employed: with light of a determined character istic and a. filmof. known. sensitivity. These and other objects of they invention will become appar.v

ent to those skilled inthe art from the. following detailed. description of exemplary forms, refer ence being. had to. the, appended drawings, in which:

Fig. 1. is a. perspective-front view of. a device constructed in accordance. with the present invention;

Fig. 2 is a perspectiverearor back view of the device;

Fig. 3 isa vertical transverse section through the device;

Fig. 4 is a partlyv diagrammatic, exploded view of. certain elements employed in. constructing. the device;

Fig. 5 is athree-quarter perspective view, partly,

broken away, of a modified form. of the devic and Fig. 6 is an enlarged transverse section of a portion. ofthedevice illustrating. a modified form of construction which maybe employed;

The device illustrated in. Figs. 1. to 4, inclusive is particularly adapted for 'use by illumination engineers and may be carried upon a suitable neck cord and is of: a sufilciently. small size to permit itsus'e as a vest pocket instrument.

Generallystated, the device'consists of a rear housing l-fl, including the baclg wall II and a substantially cylindrical side wall; 12-; this side ll e n e me a th r. i 'q 9 as; o. s um a plane or. ni 'al term 13 p ev slsl w a wi dow 14.. An eye et ma be. ar ied a outer edge 2|. The shutter member is provided with a circular recess into which the lip 16 is slidably received. One wall of such recess and the opposing surface of the lip 16 may be grooved for the purpose of receiving a malleable, preferably leaded length of bearing wire 22 which may be inserted into the grooves through a tangential opening formed in the lip of member 20, the wire or member 22 acting both to retain the shutter member 20 in position upon the housing and at the same time providing a bearing.

The shutter member 20 carries a frontal plate 23 provided with two oppositely disposed openings extending from a central point or area, one of these openings, generally indicated at 24, being delineated by the radial margins 25 and 25. whereas the other opening 21 is delineated by the radial margins 28 and 29. The imperforate, opaque sectors between margins 25 and 28 and margins 26 and 29, respectively, constitute two oppositely disposed shutters movable simultaneously with the ring-like outer shutter member 20.

These shutters overlie four color filter sectors, each of said sectors being approximately 90 degrees at its central apex. Preferably, but not necessarily, two of these filters are capable of transmitting longer lengths of wavelight, whereas the intermediate filters transmit shorter lengths of wavelight. For example, filters 36 and 30 may transmit blue light, whereas filters 3i and 3| transmit red light.

Beneath the color filters is a suitable photoelectric cell which may be of the photronic barrier-layer type generally indicated at 32. The barrier-layer of this single cell is interrupted by two intersecting some lines or channels at right angles to each other. Such channels being indi cated at 33 and 34, thereby subdividing the cell into four sections indicated at 35, 36, 31 and 38.

Mounted within the housing ill and preferably carried by the rear wall I i, as by means of suitable screws, is a microammeter or other form of galvanometer 43 provided with a needle 4!, the end of such needle being bent so as to move immediately beneath the window M of the housing. oppositely disposed portions of cell 32, such as the portions and 38, are connected to one terminal of the meter 49, whereas the other oppositely disposed portions of the cell, such as 35 and 31 are connected to the other terminal of the meter, as best illustrated in Fig. 4.

The shutter color filters and cell 32 are in closely adjacent parallel planes and the cell and color filters are suitably held in such position as by a bracket 54 secured at its lower end to a galvanometer mounting screw 55 and provided with a sleeve 56 upon which the cell 32 and filters may be fixedly mounted. The sleeve may be journaled over the pin 51 carried by the shutter 20. It is important to maintain as little clearance between the cell, color filters and movable shutter as possible.

Carried by the movable shutter 20 is a conical member 44 extending beneath the window M of the rear housing, the included angle of the cone should be substantially set to the angle of the deformed area l3. In most instances the deformed area is preferably at an angle of between about 30 degrees and degrees to the central axis about which the shutter member 20 revolves. The outer surface of this conical member 44 is suitably calibrated and carries either one or two scales, one may be calibrated in degrees Kelvin, while the other may be calibrated in terms of correction filters to be employed for one or more given types of film.

These various scales may occupy the same are on the outer surface of the scale member 44, or they may be carried on diametrically opposed areas of the scale member 44 so that either one or another of the scales may be brought into visual observation through the window it.

It will be noted that by reason of the arrangement employed the shutter member 29 can be adjusted so that the response of cells to light modulated by one type of filter is counterbalanced by the response generated by cell portions exposed to light modulated by the other filter. In other words, the index or needle 4| may be caused to assume a zero or null position; the response of cell sections 35 and 38 being opposed by the response of cell sections 36 and 3'1. Such desired null position exists when the index 4| is in alignment with a scribe line or reference line 45 traversing the window M or adjacent areas of the deformed wall portions i3 of the housing. (See Fig. 2.) The color temperature of the light reaching cell 32 can then be read directly from the indicia carried by the scale member 44, since this scale member rotates with and is a part of the shutter member 26.

Attention is also called to the fact that in event the light passing through the shutter openings is not at right angles to the plane of the surface of cell 32, but instead is inclined thereto, the reading will not be dropped or varied to any material or appreciable extent. If, for example, light is passing through the shutter openings from the left it will be apparent that some light can get under the edge 26 and therefore more light will pass through the red filter than in the event the light is more normal and at right angles to the cell. However, any increase in the amount of light passing beneath the edge 26 is compensated for by the reduction in the amount of light passing the edge 28 and the red filter underlying such edge.

This self-compensating feature of the device is extremely important since it eliminates the necessity for very carefully pointing the instrument directly at the light being tested. Attention is also called to the fact that by providing the window 14 at an angle to the axis, the operator need not look toward the light being tested and his vision is thus not impaired.

' Fig. 5 shows a somewhat amplified form of device wherein the cell 32' is divided into two sections, only one of the sections being covered with a red filter 3|" and the other with a blue filter 30", these two sections being then connected to opposing terminals of the microammeter.

The shutter member 20' is provided with a semi-circular aperture or opening having a serrated edge 5B. The shutter member 23' carries an inner conical indicia member such as 44 in the previous embodiment, the scale on such member 44 cooperating with a window and the index member of the microammeter. The form of device illustrated in Fig, 5 operates in substantially the same manner, but has to be accurately directed toward the light being tested since it does not have the self-compensating features previously described in connection with the first embodiment.

It may be noted that the edges 25, 26, 28 and 23 of the openings 24 and 21 of the shutter member 23 may also be serrated in the manner illustrated in Fig. 5 for the purpose of imparting greater accuracy to the readings.

Fig. 6 illustrates a form of construction which.

may be. employed-in or the devicesshereina as the shutter member 20" is provided with an externally threaded surface 5|. A flanged outer ring 52 engages tl'le-lipl'6 and is threaded onto the threaded; edglaili of'gthe shutter member so as toslidably grasp the lip, L6 of the housing, A ma l setscre 5.3- may be. used to hold. the flanged ring 52 in fixed position, with respect ohc, shutt r m r 20'? after. the e ice is assembl d...

Al hou h. or pu p s s o s mp c tion, ef.- erenca has. been made to filtersgand cell, portions of an area, each ncludin 90.. de rees, asilluStrated in Fig. 4', it is not necessary. that the. dand; t r reasbe of. equal size. Depending. upon the transmission, characte listi'cs oi the. fi ters employed; e. r -.a d b uefilters mayvaly in relati've size.

All'changes and modifications coming within the scope of theappcnded claims are embraced thereh3.-

l cla-im:v I

1;. compact, direct-reading photometric; device comprising: a rear housingincluding a back Wall and forwardly directed side wall portions terminating ina; circular lip. lying. ma planepa-r- 31181: to the. back. wall, a. section of; the side: wall being inclined to the} back; wall. and, lip; and; ro: videdwith awindowr port; a. sin hutter-member engaging said circular lip for rotation, there on, said shutter member being provided with an opening of fixed area eccentrically disposed with respect to the axis of rotation; a conical scale member carried by the shutter member and extending beneath the window port, indices carried by the scale member for visual observation through the window port; and a stationary, lightresponsive means within the housing including a response-indicating meter provided with an index extending between the window port and scale member, said light-responsive means including at least two cell and filter assemblies, said cells being connected in opposed relation, each filter covering a cell, said filters being capable of transmitting selected spaced wave length bands of light, the area of a cell and filter assembly being virtually equal to the area of said shutter opening, one cell and filter assembly being adapted to be fully exposed when the shutter opening is aligned with said assembly, said cell and filter assemblies being so arranged for simultaneous partial exposure as said shutter opening is moved thereacross for measuring the ratio of energy in the wave length bands of light transmitted by the filters.

2. A compact, direct reading photometric device comprising: a rear housing including a back wall and forwardly directed side wall portions, a section of the side wall being inclined to the back wall and provided with a window port; circular edge margins provided on said side wall portions; a shutter member engaging said circular edge margins for rotation thereon and extending :between said side wall portions, said shutter member being provided with a sector-like opening; a stationary light-responsive assembly within the housing including a plurality of contiguous sector-like cells and a response indicating meter provided with an index, adjacent cells being connected to the meter in opposing relation to', give a null reading; a plurality of sector-shaped light filters, each being capable of transmittinga differentwave length band and covering a respecto; cause? the, sectorike or ,I: o; multan r ously tra erse ad acent filt rs; ndv cells co re -i thereby: in. posure varying lation; a d ells;

light. filters and! sector-like open sy n in. cl sely adjacent: parallel: planes and: a hh s o virtually thesame sector-shape; and-pa scale-member.- carried by and rotatable with the shutter member in visually observable relation to; the window port, saidi index extending between thewindowportand scale member.

32-. a. compact portable p o ometr c, dev ce and: a meter o erably conne ted to the index,

the provision, of: a light-responsive meansone erably connected to.the meter and including a;

plurality ofrsector-shaped cell's arranged in circular sequence; a plurality oi? light filters, each covering the entire area. of; a respective cell, adjaoent light". filters being capable of transmitting different wave length bands; adjacentcells, of

said light-responsive means being connected. in opposing relation; and" a shutter means mounted for? rotation and'comprisi-n'g a wall providedwith means'fcr admitting light'to said light-.responsive means through said filters, said light-admitting means havin fixed non-variable open area of virtually the same area and shape as two noncontiguous cells and associated-filters and adapted to traverse simultaneously said'cells and associated filters in complementary exposure varying relation upon rotation of; said shutter means.

4. A device as defined in claim 3 wherein said light-admitting means in said shutter means is virtually equivalent in area to the total area of two of said cells.

5. A device as defined in claim 3 wherein said light-admitting means in said shutter means includes diametrically opposed openings, each of equal area.

6. A device as defined in claim 3 wherein said light-admittin means in said shutter means includes spaced openings, each disposed to normally cooperate with a cell and associated filter of different wave length transmission than the cell and asosciated filter cooperating with the adjacent opening.

7. In a compact, portable photometric device including a housing provided with a window, a scale and a movable index beneath the window, and a meter cooperating with the index, the provision of light responsive means operably connected to the meter and including a plurality of cells of virtually equal area sequentially arranged; a plurality of light filters, each covering a respective cell and equivalent in area therewith, alternate light filters being capable of transmitting the same wave length bands and adjacent light filters difierent wave length bands; adjacent cells of light-responsive means being connected in opposed relation; and shutter means relatively movable with respect to said light-responsive means and filters, said shutter means minating in a circular lip lying in a, plane parallel to the back wall, a section of the side wall being inclined to the back wall and lip and provided with a window port; a single shutter mem ber engaging said circular lip for rotation thereon, said shutter member being provided with two opposing sector-like openings of fixed area; a stationary light-responsive assembly within the housing including two pairs of sector-like cells, each cell corresponding in shape to said sectorlike openings; and a response-indicatin meter provided with an index, each pair of cells being connected to the meter in opposing relation to ive a null reading; and a pair of light filters having different spectral transmission for each pair of cells, said shutter member being selectively positionable to simultaneously vary the exposure relationship of each pair of filters and cells; said cells, light filters and shutter lying in closely adjacent parallel planes; and a scale member carried by the shutter member in virtually observable relation to the window port, said meter index extending between the Window port and scale member.

9. A photometric device of the character stated in claim 8 wherein the area occupied by one of said filters is substantially equal to the area occupied by the other of said filters each area being substantially equal to the area of a sector-like opening in the shutter and to the area of a cell beneath the filter.

10. A photometric device of the character stated in claim 8 wherein the number of cells is twice the number of openings in the shutter mem- 8"? her, eachcell being covered by a light filter, said filters occupying adjacent areas of a common plane and arranged in a circularly arranged sequence.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,895,385 Townsend et al. Jan. 24, 1933 2,185,690 Lane Jan. 2, 1940 2,203,036 Briessen et al June 4, 1940 2,297,428 Nuchterlein Sept. 29, 1942 2,298,667 Weymouth Oct. 13, 1942 2,307,504 Hastings Jan. 5, 1943 2,308,095 Meeder Jan. 12, 1943 2,319,212 Cooley May 18, 1943 2,330,877, Fleischer et al Oct. 5, 1943 2,455,116 Gittus Nov. 30, 1948 2,462,823 VVOodward Feb. 22, 1949 2,482,281 Lingel Sept. 20, 1949 FOREIGN PATENTS Number Country Date 508,802 Great Britain July 5, 1939 925,985 France -Q Apr. 14, 1947 OTHER REFERENCES Electronics, March 1937, pages 28, 29, article by Richter. 

